Abstract Co-existing neuropsychiatric symptoms (NPS) in patients with mild cognitive impairment (MCI), especially those worsening over time, are associated with more rapid cognitive and functional decline and a greater risk of Alzheimer's disease (AD). Optimal NPS management, meaning effectively managing multiple NPS simultaneously, requires a solid understanding of the shared neural mechanism across NPS. The goal of this proof-of-concept mechanistic intervention study is to validate the causal relationship between a NPS-shared neural circuit we previously discovered and various NPS. We will modify a key region within the NPS-shared neural circuit [i.e. left precentral gyrus (LPG), critical for regulating visual attention] with anodal transcranial direct current stimulation (tDCS). Our central hypothesis is that an activation of LPG and a reorganization of NPS- shared neural circuit will link to improvement in multiple NPS. Using a Stage 0 pilot randomized control trial design we will recruit n = 40 older adults with informant-rated NPS that has worsened in the past 2 years, which is considered the most detrimental type of NPS in MCI. We will assign participants to 4-week active anodal vs. sham LPG online tDCS group. We will assess resting-state and visual attention task-related functional MRI and informant-rated NPS at baseline, and the end of week 4 and week 8, and diffusion MRI at baseline. The two primary aims are to determine the effect of tDCS on NPS-shared neural circuit (Aim 1), as well as the relationship between NPS-shared neural circuit and informant-report NPS (Aim 2). The exploratory aim will be to examine the relationship between NPS and the coherence between structural and functional aspects of the NPS-shared neural circuit. Probing the LPG via anodal tDCS provides a way to experimentally test the causal relationship between our previously discovered NPS-shared neural circuit and informant-rated NPS. The proposed research is highly innovative, while scientifically grounded, for targeting one brain region that may affect multiple NPS. Validating the hypotheses has the potential for future R01 study that directly conducts a Stage 2 trial addressing NPS in MCI, and thus ultimately improves patient's quality of life and reducing caregiving burden.